In an electrophotographic image forming apparatus, there has been known a structure in which elements such as a photosensitive member drum and a developing roller as a rotatable member related to image formation are integrated into a cartridge and can be mounted to and dismounted from an image forming apparatus main assembly (hereinafter, the apparatus main assembly). With such a structure, in order to rotate the photosensitive drum in the cartridge, a structure that receives driving force from the apparatus main assembly is employed in many apparatuses. And, there is known a structure in which a driving force is transmitted by engaging a coupling member with a driving force transmitting portion such as a driving pin on the apparatus main assembly side on the cartridge side.
For example, Japanese Unexamined Patent Application Publication No. 2008-233867 discloses a cartridge including a coupling member provided at an end portion of the photosensitive drum so as to be tiltable with respect to the rotation axis of the photosensitive drum.